Ionic vacuum pump



IONIC VACUUM PUMP Filed Jan. 20, 1964 2 Sheets-Sheet l FIG. 1

INVENTORS LEWIS A. DAVIS RICHARD T. MORRIS ATTORNEY Feb. 22, 1966 L. A.DAVIS ETAL 3,236,442

IONIC VACUUM PUMP Filed Jan. 20, 1964 2 Sheets-Sheet 2 M INVENTORS LEWISA. DAVIS RICHARD T. MORRIS ATTOR N EY United States Patent OfiticePatented Feb. 22, 1966 3,236,442 IONIC VACUUM PUMP Lewis A. Davis, CostaMesa, and Richard T. MOl'l'lS,

Inglewood, Calif., assignors to Morris Associates, Hawthorne, Calif., apartnership Filed Jan. 20, 1964, Ser- No. 338,701 Claims. (Cl. 230-69)This invention relates to an ionic vacuum pump and more particularly tosuch a device utilizing a cold cathode discharge which is capable ofachieving an evacuation of gas to extremely low pressure levels.

In achieving the extremely low pressures required in such devices asvacuum tubes, linear accelerators and the like, ionic pumps aregenerally utilized. With this type of device, mechanical pumping isfirst used to evacuate most of the gas, and then the final pumpingaction is achieved electronically in what has become to be known in theart as ionic pumping. In most ionic pumps of the prior art, a glowdischarge is generated by placing a high potential between an anode andcathode contained within the chamber to be evacuated. The anode andcathode are both made of a reactive metal such as titaniurn. Elec ronsemitted from the cathode are accelerated at high velocity towards theanode. The electrons collide with gas molecules thereby producingionization of such molecules. The gas ions so formed bombard the cathodecausing atoms to be sputtered (knocked off) the surfaces thereof. Thesesputtered atoms are attracted to the anode and there form stablechemical compounds with active gas atoms remaining in the chamber.

In these devices of the prior art, it has been found that a greatincrease in pumping efiiciency can be achieved if a magnetic field isapplied to the electrons flowing between the cathode and anode. Theapplication of such a magnetic field causes the electrons to take arelatively long circular path which causes them to collide with a greatmany more gas molecules than if a direct path were followed. A typicaldevice of the prior art in which such ionic pumping is achieved isdescribed in Patent No. 2,755,014 issued July 17, 1956, to W. F.Westendorp et a1. With this type of device, ultra high vacuum pumpingcan be achieved.

Prior art devices have a significant limitation in that it takes arelatively long period of time to achieve the desired pumping action.This severely curtails the effective utilization of the pump. It hasbeen found that the major factor limiting the pumping speed is the overheating of the reactive metal cathodes during the high ion currentplasma discharge when the ionic pumping is first started after themechanical pumping has been completed. Such heating releases gasformerly trapped by ion burial and physical absorption from the previouspumping cycle causing a substantial increase in the ion bombardment ofthe electrodes thereby resulting in a high pressure equilibriumcondition. It therefore is apparent that pumping efficiency could beincreased substantially if this heating action could be minimized. Whilethis problem has been recognized, the provision of completely adequatecooling means has been discarded in the prior art as being toocomplicated to be feasible.

Further, in achieving the desired circular motion of the electrons, highstrength permanent magnets have generally been utilized in the devicesof the prior art. Such magnets while completely effective in producingthe desired circular electron path, tend to be rather costly and inaddition are generally rather heavy and bulky. The magnets generallyutilized also have the disadvantage that they produce stray magneticfields. This presents a problem in the utilization of such a prior artpump to evacuate equipment while it is operating, such as in the case oflinear accelerators, in view of the fact that this type of electron beamconcentrating equipment will not function properly with stray magneticfields present.

The device of this invention overcomes the above enumerated shortcomingsof prior art ionic pumps by providing simple yet highly effective meansfor cooling the pump and utilizing a periodic magnetic stack forgenerating the desired magnetic field, such stack being comprised ofrelatively inexpensive compact and lightweight magnet units. Theperiodic magnet stack highly concentrates the flux and produces few orno stray magnetic fields, which might adversely affect the operation ofequipment in the vicinity.

The above enumerated improvement is achieved in the device of theinvention without resorting to an expensive or complicatedconfiguration. The device of the invention is capable of beingconstructed of simple, relatively inexpensive components which can bereadily disassembled and reassembled for the replacement of componentssuch as for example, cathode and anode units.

The desired cooling is achieved in the device of the invention byutilizing a cold trap which is centrally located within the pumphousing. In this cold trap, is contained a cryogenic type refrigerant.Also contained within the cold trap is the periodic permanent magnetstack. The vacuum chamber is located between the walls of the cold trapand the walls of the container.

Externally concentric with the magnet assembly within the vacuum chamberare a plurality of alternately positioned anode and cathode members. Thecathode members are each attached to a separate pole piece unit andthese pole piece-cathode assemblies are supported in the housing by themagnetic force of the magnet stack. The anode members are connected tobracket members which are supported on the end cathode-pole piecemembers. Both the anode and cathode members are thus magneticallysupported.

It is therefore an object of this invention to provide an improved ionicvacuum pump.

It is another object of this invention to provide an ionic vacuum pumpwhich can readily be assembled and disassembled.

It is a further object of this invention to provide an ionic vacuum pumpcapable of higher efficiency and substantially faster pumping actionthan prior art devices.

It is still another object of this invention to provide an ionic vacuumpump of simple configuration in which cryogenic cooling is provided.

It is still another object of this invention to provide an ionic vacuumpump in which a periodic permanent magnet stack is utilized to generatea magnetic field and the anode and cathode members are supported by themagnetic force of the stack.

It is still a further object of this invention to provide an ionicvacuum pump of high efiiciency which is both simple and economical tofabricate.

Other objects of this invention will become apparent from the followingdescription taken in connection with the accompanying drawings of whichFIG. 1 is a perspective view with partial cutaway section of a preferredembodiment of the device of the invention, and

FIG. 2 is a cross sectional view taken along the plane indicated by theline 22 in FIG. 1.

Referring now to the figures, cylindrical housing 11 which is fabricatedof a non-reactive metal such as stainless steel is utilized to house thedevice. Housing 11 has a cover 12 which provides an airtight seal forchamber 30 which is formed therein. Cover 12 is removably attached tothe housing by means of bolts 14 which are fixedly attached to collar 19and nuts 16 which matingly engage the threaded top portions of thebolts. Collar 19 is slidably mounted on housing'll so that it can beremoved from the housing along with the bolts. Collar 21 which isfabricated of a soft metal such as copper is fixedly attached to housing11 as, for example, by brazing. The sealing action is achieved by meansof knife edge seal 18 which tightly abuts against soft collar 21 whennuts 16 are tightened down.

Fixedly attached to cover 12 in a gas tight joint therewith is containerwhich is fabricated of a non-reactive metal such as stainless steel.Such attachment may be achieved by any suitable means such as, forexample by welding. Container 20 serves as a cold trap, and inoperation, a cryogenic liquid 17 such as liquid nitrogen is heldtherein. The top portion 22 of container 20, the end of which is exposedto the atmosphere, preferably is restricted as in the bottleneckconfiguration shown in the figures to minimize the evaporation of thecryogenic liquid.

Within container 20, is a periodic permanent magnet stack which includestoroidal shaped magnets 23a-23e. The magnets are arranged in a periodicarray with their poles positioned as indicated in FIG. 2. This in effectprovides a parallel aiding configuration for adjacent magnets which, aswell known in the art, gives a very high flux concentration with minimalleakage, thereby substantially eliminating stray magnetic fields.Excellent results have been achieved with ceramic toroidal magnetsfabricated of a low permeance material such as barium ferrite. Suchceramic type magnets are available, for example, from the GeneralMagnetic Corp., Detroit, Michigan. Sandwiched between the magnets and atthe top and the bottom of the stack are washer shaped pole pieces 28which are fabricated of magnetic material. The magnet stack and theassociated pole pieces rest freely inside container 20 and are notattached thereto. They are placed inside the container when it isfabricated and are not removable therefrom. As these units seldom needreplacement even after long periods of operation, such construction isentirely practicable.

Each of magnet members 23a23e has a slot therein (not shown) runningfrom the center of the magnet through to the wall of container 20. Thisis to permit the cooling liquid 17 to flow through to the walls of thecontainer to cool the cathode members adjacent thereto.

Located between the outer wall of container 20 and the inner wall ofhousing 11 is vacuum chamber 30. Vacuum chamber 30 is connected to theequipment to be evacuated by means of flange member 32 which is fixedlyattached in gas tight relationship to cover 12. Located within vacuumchamber 30 are cathode-pole piece assemblies 33. These assemblies whichare washer shaped and are externally concentric with container 20,comprise inner magnetic pole pieces 34 and outer cathode pieces 35 whichare fixedly attached to the pole pieces as, for example, byspot-welding. Pole pieces 34 are fabricated of a highly magneticmaterial while cathode pieces 35 are of a reactive metal such astitanium.

Cathode-pole piece assemblies 33 are held in position between the magnetunits 23a-23e opposite pole pieces 28. Assemblies 33 are held inposition centered between the magnet units by virtue of the magneticforce of such magnets, .a flux path being provided from the north poleof each magnet through an adjacent pole piece 28 thence through anadjacent cathode pole piece 33, from there through an associated anodemember 39 to the next succeeding pole piece 33, and thence back througha centrally located pole piece 28 to the south pole of the magnet. Thus,an eflicient flux path is provided through the electron flow area toproduce maximum magnetic effect in deflecting the path of the electrons.This mag netic flux also holds the cathode assemblies 33 in position.

Anode assemblies 39 are ring or washer shaped in configuration and arearranged between the cathode assemblies 33 in external concentricitywith container 20. Anode assemblies 39 comprise a pair of oppositelypositioned cylindrical members 40 between which a corrugated member 41is contained. Corrugated member 41 is fixedly attached to cylindricalmembers 40, as for example by welding. Members 49 and 41 are fabricatedof a reactive metal such as titanium.

Anode assemblies 39 are spot welded at points 45 to bracket members 46and 47 to form a unitary assembly. Bracket members 46 and 47 areattached by means of screws 50 to support insulators 53a, 53b, and 53c,53d respectively. Insulators 53a, 53d are attached to the bottom ofcathode-pole piece assembly 33b by means of screws 55, while insulators53b and 530 are attached to the top cathode-pole piece assembly 33t bymeans of screws 56. The anode units are thus supported on the top andbottom cathode-pole piece assemblies which in turn are held in place bythe magnet stack. Both the cathode and anode assemblies are thusmagnetically supported.

Bracket 47 also acts to conduit high voltage to the anode assemblies andis connected to high voltage terminal 6i} by means of connector member49. The feed through assembly 61 for terminal 60 provides a high vacuumseal which assures that there is no air leakage to chamber 30. Endcathode-pole piec assemblies 33b and 33t have no cathode pieces 35 onthe ends facing in sulators 53a53d and act to shield these insulatorsand high voltage terminal 61 from sputtered material which mightotherwise accumulate thereon and cause the high voltage to shortcircuit.

In operation, flange member 32 is attached to the equipment to beevacuated in gas-tight relationship therewith. Evacuation is firstaccomplished by mechanical pumping to the best of the capabilities of asuitable mechanical pumping device (not shown). A high voltagepotential, e.g. in the neighborhood of 5,000 volts is then placedbetween terminal 60 and the wall of housing 11. This causes an electronflow between cathode members 35 and anode members 39. The paths theelectrons take between the cathode and anode members is increasedsubstantially by the magnetic action of the magnet stack 23a- 23e whichimparts a circular path to such electrons caus ing them to collide witha substantially greater number of gas molecules than if a direct pathwere taken.

The positive ions produced by the collision between the gas moleculesand the electrons are aitracted to the surfaces of cathode members 35and bombard the surfaces of these cathode members sputtering off atomstherefrom. During the initial stages of operation, when there are arelatively large number of gas molecules chamber 30, this bombardmentaction is quite heavy and tends to cause the cathodes to heat upsubstantially. This heating tends to release gas which was formerlytrapped by ion burial and physical absorption. In the device of thisinvention, such heating is minimized by the cooling action of cryogeniccoolant 17, and such addition of gas to chamber 38, which would greatlyslow up the pumping action, is thereby substantially eliminated.Experimentation indicates that in the device of the invention, the samedegree of evacuation can be achieved in ten minutes that Without coolingwould take an hour and a half. It is also indicated that the coolingaction achieved in the device of the invention tends to prolong theuseful life of anode and cathode units, improves the efficiency of themagnet stack, and enables a higher degree of evacuation. The coolantevaporates through the open top of container 20 and can readily bereplaced as required.

The cathode-pole piece and anode assemblies can be removed forreplacement merely by loosening and removing nuts 16 and taking cover 12off housing 11. The anode and cathode units can readily be disassembledby detaching the screws holding together the bracket members and theirassociated insulators.

Thus, the device of the invention provides a simple and compact yethighly efficient ionic vacuum pump. A highly concentrated magnetic fieldhaving minimal stray fields is provided by means of a relativelyinexpensive magnetic stack, this stack also being used to support theanode and cathode assemblies. A marked increase in the speed of pumpingaction is achieved by virtue of the utilization of cryogenic cooling.

While the device of the invention has been described and illustrated indetail, it is to be clearly understood that this is intended by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of this invention being limited only bythe terms of the following claims.

We claim:

1. In an ionic pump,

a pump housing,

a container centrally located within said housing,

means for generating a magnetic field located within said container,

a cryogenic coolant contained within said container,

a vacuum chamber being formed between the outer walls of said containerand the inner walls of said housing,

an anode assembly and a cathode assembly contained within said vacuumchamber, and

means for supporting said anode assembly and said cathode assembly inexternal concentricity with said container.

2. In an ionic pump,

a pump housing,

a container located within said housing,

means for generating a magnetic field located within said container,

a cryogenic coolant contained within said container,

a vacuum chamber being formed between the outer walls of said containerand the inner walls of said housing,

an anode assembly and a cathode assembly contained within said vacuumchamber, and

means for supporting said anode assembly and said cathode assembly inexternal concentricity with said container, said supporting meanscomprising said means for generating a magnetic field.

3. In an ionic pump,

a pump housing,

a container located within said housing,

means for generating a magnetic field located within said container,said means for generating a magnetic field comprising a periodicpermanent magnet stack,

a cryogenic coolant contained within said container,

a vacuum chamber being formed between the outer walls of said containerand the inner Walls of said housing,

an anode assembly and a cathode assembly container within said vacuumchamber, and

means for supporting said anode assembly and said cathode assembly inexternal concentricity with said container.

4. In an ionic pump,

a pump housing,

a container located within said housing,

means for generating a magnetic field located within said container,

a cryogenic coolant contained within said container,

a vacuum chamber being formed between the outer walls of said containerand the inner walls of said housing,

an anode assembly and a cathode assembly contained within said vacuumchamber, said anode assembly and said cathode assembly being washershaped, said cathode assembly comprising a washer shaped memberfabricated of magnetic material sandwiched between a pair of washershaped members fabricated of a reactive metal, and

means for supporting said anode assembly and said cathode assembly inexternal concentricity with said container.

5. An ionic vacuum pump comprising a housing,

cover means for said housing,

container means centrally located within said housing, said containermeans having aperture at one end thereof said aperture passing throughsaid cover means,

a periodic permanent magnet stack contained within said container means,

a coolant contained within said container means,

a vacuum chamber being formed between the outer wall of said containermeans and the inner wall of said housing,

a plurality of cathode-pole piece assemblies, said cathode pole pieceassemblies being externally concentric with said container means, eachof said cathode-pole piece assemblies being held in place magneticallybetween a pair of adjacent magnetic poles of said magnet stack,

a plurality of anode assemblies, each of said anode assemblies beinginterposed between a pair of said cathode-pole piece assemblies, and

means for supporting said anode assemblies on at least one of saidcathode-pole piece assemblies.

6. The pump as recited in claim 5 wherein said means for supporting saidanode assemblies comprises a pair of brackets fixedly attached to eachof said anode assemblies, and insulator means for attaching saidbrackets to the uppermost and lowermost cathode-pole piece assemblies.

7. An ionic vacuum pump comprising a housing,

covers means forming a gas tight seal for said housing,

container means centrally located within said housing, said containermeans having an aperture formed at one end thereof, said one end of saidcontainer means passing through said cover means,

a periodic permanent magnet stack contained within said container means,

a coolant contained within said container means,

a vacuum chamber being formed between the outer wall of said containermeans and the inner wall of said housing,

a plurality of integrally formed washer shaped cathodepole pieceassemblies, said cathode-pole piece assemblies being externallyconcentric with said container means, each of said cathode-pole pieceassemblies being held in place magnetically between a pair of adjacentpoles of said magnet stack,

a plurality of washer shaped anode assemblies, and

means for holding said anode assemblies together to form an integralunit, said anode assemblies being interposed between said cathode-polepiece assemblies.

8. The pump as recited in claim 7 and additionally including means forattaching said anode assemblies holding means to a pair of saidcathode-pole piece assemblies.

9. The pump as recited in claim 7 wherein said container, said housingand said magnet stack are cylindrical in shape and are in concentricitywith each other and said cathode-pole piece and anode assemblies.

10. The pump as recited in claim 7 wherein said anode assemblies eachcomprise a pair of concentric cylindrical members and a corrugated platemember positioned between said cylindrical members and fixedly attachedthereto, said plate member forming a ring in concentricity with saidcylindrical members.

11. The pump as recited in claim 7 wherein said magnet stack comprises aplurality of torroidal magnet units.

12. In an ionic pump,

a pump housing,

a cylindrical container centrally mounted in said housmagnet means forgenerating a magnetic field located within said container,

a cryogenic coolant contained within said container cover means forforming a vacuum chamber between the outer walls of said container andthe inner walls of said housing,

a plurality of alternately spaced anode and cathode-pole pieceassemblies contained within said Vacuum chamber, said anode and cathodeassemblies being washer shaped, and

means including said magnet means for supporting said anode andcathode-pole piece assemblies in a stacked arrangement in externalconcentricity with said container.

13. An ionic vacuum pump for producing an ultra high vacuum comprising ahousing,

a cover for said housing,

a container fixedly attached to said cover substantially at the centerof said cover, said container having an open end, said open endprotruding through said cover,

means for removably attaching said cover to said housing in gas tightrelationship thereto to form a gas tight chamber between the walls ofsaid container and the Walls of said housing,

a coolant contained within said container,

a plurality of cathode members fabricated of reactive metal located inexternal concentricity to said container,

pole piece members fixedly attached to said cathode members,

a plurality of anode members fabricated of reactive metal interposedbetween said cathode members and in external concentricity with saidcontainer,

means for connecting a high voltage potential between said anode andcathode members,

means for mounting said anode members on at least one of said cathodemembers in insulated relationship thereto, and

magnet means contained within said container for gen erating a magneticfield to cause electrons flowing between said cathode and anode membersto follow a circular path and to magnetically hold said pole piecemembers, thereby supporting said cathode and anode members.

14. The pump as recited in claim 13 wherein said magnet means comprisesa periodic permanent magnet stack.

15. The pump as recited in claim 13 wherein said coolant comprises acryogenic liquid.

References Cited by the Examiner UNITED STATES PATENTS 2,755,014 7/1956Westendorp et al. 23069 2,983,433 5/1961 Lloyd et a1 230-69 2,993,6387/1961 Hall et a1 23069 3,018,944 1/1962 Zaphiropoulos 23069 3,117,2471/1964 Jepsen 23069 X DONLEY J. STOCKING, Primary Examiner.

WARREN E. COLEMAN, Examiner.

1. IN AN IONIC PUMP, A PUMP HOUSING, A CONTAINER CENTRALLY LOCATEDWITHIN SAID HOUSING, MEANS FOR GENERATING A MAGNETIC FIELD LOCATEDWITHIN SAID CONTAINER, A CRYOGENIC COOLANT CONTAINED WITHIN SAIDCONTAINER, A VACUUM CHAMBER BEING FORMED BETWEEN THE OUTER WALLS OF SAIDCONTAINER AND THE INNER WALLS OF SAID HOUSING, AN ANODE ASSEMBLY AND ACATHODE ASSEMBLY CONTAINED WITHIN SAID VACUUM CHAMBER, AND MEANS FORSUPPORTING SAID ANODE ASSEMBLY AND SAID CATHODE ASSEMBLY IN EXTERNALCONCENTRICITY WITH SAID CONTAINER.